Lipid membranes in living cells facilitate non-polar chemistry in an aqueous environment by forming microscopic spaces friendly to fat-soluble compounds.

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Unlike modern industry, biological systems are capable of performing complex chemistry with both water-soluble (polar) and oily (non-polar) compounds in a water-based environment. Most industrial operations, however, rely on often toxic chemical solvents to perform complex reactions with non-polar substances. Organisms have evolved the ability to manipulate non-polar molecules in water because they have no other choice--Earth is a water-based environment. They've achieved this feat by developing what could be referred to as “micro environments” that provide non-polar substances a favorable molecular-sized, water-soluble envelop including globular proteins, lipid bilayers, and micelles.

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"Compounds containing both strongly polar and strongly nonpolar groups are called amphiphilic molecules (from the Greek amphi meaning “both” and philos meaning “loving”). Salts of fatty acids are a typical example that has biological relevance. They have a long nonpolar hydrocarbon tail and a strongly polar carboxyl head group, as in the sodium salt of palmitic acid. Their behavior in aqueous solution reflects the combination of the contrasting polar and nonpolar nature of these substances. The ionic carboxylate function hydrates readily, whereas the long hydrophobic tail is intrinsically insoluble. Nevertheless, sodium palmitate and other amphiphilic molecules readily disperse in water because the hydrocarbon tails of these substances are joined together in hydrophobic interactions as their polar carboxylate functions are hydrated in typical hydrophilic fashion. Such clusters of amphipathic molecules are termed micelle." (Garrett and Grisham 2010:33)

BiochemistryJanuary 5, 2012
Reginald H. Garrett

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